This was back in 1991 or 1992 or so, certainly before 1994 when the NS steam program was cancelled.
The consist wasn't made up of Amtrak cars, but vintage N&W cars belonging to NS and various NRHS chapters. All original, no holding tanks.
Possibly had the steam program lasted past 1994 the cars might have been retro-fit with holding tanks, but to my knowledge at the time none had them.